As it is known, in portable mobile applications HDD devices are more and more frequently incorporated into personal electronic and personal computer products. This is because HDD high capacity, fast speed, and low price combination surpasses any other memory product, making them the best choice for data storage in portable apparatuses, such as laptop computers, Personal Data Assistants (PDAs), digital audio players, mobile phones, digital cameras, and the like.
FIG. 1 shows schematically the structure of a typical HDD device 1. In a per se known manner, the HDD device 1 comprises: a rotating disk 2, provided with a magnetic thin film as a data-storage medium and being rotated around an axis by a spindle motor (not shown); a read/write head 3 which is carried by an arm 4 and is suspended over the rotating disk 2, and which comprises a magnetic transducer that magnetically transfers information to and from the data-storage medium; a voice coil motor driver 5 for moving and positioning the arm 4 over the rotating disk 2; a parking ramp 6; and a microprocessor controller 7 for controlling operation of the HDD device 1, and particularly of the voice coil motor driver 5 and the spindle motor. When in operation, the read/write head 3 is positioned over specific locations of the rotating disk 2 for reading data from and writing data to the associated data-storage medium. Under certain circumstances, such as when the HDD device 1 is in power down or in low power consumption mode, the read/write head 3 is moved away from the surface of the rotating disk 2 and parked in a detent position at the parking ramp 6.
Due to their portable nature, the above electronic portable apparatuses are accident prone and may easily undergo violent impacts, in particular in the case where they are dropped onto the floor during normal use. In the case of a fall, the impact of the portable apparatus with the ground has repercussions on the associated HDD device 1, in the worst case producing damage and consequent permanent loss of data. In fact, the HDD device 1 is very sensitive to impact, in so far as, in order to ensure its proper operation, the read/write head 3 is normally kept at a very small distance from the associated data-storage medium. Consequently, in the case of an impact, the read/write head 3 collides with and may get damaged together with the data-storage medium, causing irreversible loss of the data stored within.
To prevent, or at least limit, the occurrence of the above destructive events, HDD protection systems based upon the detection of a condition of free-fall of the portable apparatuses have been proposed.
As it is known, an object is considered to be in free-fall when it is falling under the only influence of gravity; in other words, any object which is moving and being acted upon the sole force of gravity is said to be in a state of free-fall. The following is the module of the free-fall equation of an object which is in free-fall condition, assuming a zero velocity at the beginning of the fall:
  h  =            1      2        ·    g    ·          t      2      where h is the initial height of the fall, g is the acceleration of gravity (9.81 m/s2), and t is the fall time. By way of example, and using the above equation, a fall time of about 378 ms can be calculated from a typical desktop height of about 0.7 m. An impact deceleration force can also be calculated using the following equation:
  A  =            π      ·      R      ·                        2          ·          g          ·          h                            2      ·      t      
The table of FIG. 2 shows the impact deceleration force A (normalized to the g value), and fall time t based on the height h of the fall, assuming a rebound factor of 1.5 (where 1 means no rebound, and 2 means 100% rebound) and a shock duration of 2 ms.
In particular, following upon a free-fall detection, the above HDD protection systems issue appropriate actions for protecting the electronic portable apparatus, e.g. they command for retracting the read/write head 3 from the disk surface up to the positioning ramp 6. As a result, upon impacting the ground of the HDD device 1, the read/write head 3 and the rotating disk 2 do not collide, thus preventing the HDD device 1 from damage, or in any case limiting the extent of such damage.
For example, considering that a typical HDD device of a portable PC system can sustain 800 g non operating shocks and 225 g operating shocks, from the above table it follows that the HDD device can sustain impact if it falls from height below 0.178 m. The HDD device can not sustain impact if it falls from height above 2.282 m, because the impact deceleration force A is over the non operating shock level. With the above protection systems, the HDD device may sustain fall impact between 0.178 m to 2.282 m by placing the read/write head 3 to the ramp position, therefore greatly reducing the possibility of damage and loss of data.
In greater detail, the free-fall condition of the portable electronic apparatus is detected by using an acceleration sensor, fixed to the portable electronic apparatus. In particular, a free-fall condition is detected when the magnitude of the acceleration vector calculated from the acceleration sensor output falls within a preset range of values. In general, since it is not possible to determine the orientation of the portable apparatus during its free-fall, a three-axis acceleration sensor is used, the acceleration vector being the vector sum of the acceleration components along three mutually orthogonal axes.
To obtain an efficient protection against impact, the free-fall condition must be detected in the shortest time possible so as to enable subsequent activation of the appropriate actions of protection. In known HDD protection systems, a microprocessor is used to poll and to acquire the acceleration sensor outputs, to calculate the acceleration vector and its magnitude, and to compare the calculated magnitude against to a pre-programmed threshold value. In particular, the main microprocessor of the portable electronic apparatus that it is desired to protect or the controller of the HDD device, or even a dedicated microprocessor are used for this purpose.
A solution of this sort does not always enable detection of the condition of free-fall with a promptness sufficient to prevent damage to the portable electronic apparatuses. In fact, if the main microprocessor of the portable electronic apparatus, or the microprocessor of the HDD device controller are used, the same microprocessors must perform a plurality of functions, and are used in “time sharing” by the various resources and cannot dedicate the majority of their computing power and time to monitoring the output of the accelerometer. It follows that the free-fall event can occur during a time interval in which the microprocessor is occupied to manage other resources, and the free-fall can thus be detected too late to avoid damage to the portable electronic apparatus. Also, even if a dedicated microprocessor is used (solution that can be anyway too expensive for most applications), if the free-fall event happens in between two consecutive acquisition cycles, there is a latency time before the free-fall event can be reported (the worst latency time being a full sample time interval). In addition to this latency time, microprocessor instructions execution time (e.g. for the calculation of the vector sum and magnitude thereof) also needs to be accounted for the overall free-fall detection time.
The aim of the present invention is to provide a free-fall detection device and a free-fall protection system for a portable electronic apparatus which are free from the drawbacks referred to above and in particular operate in a more reliable way, and allow for a prompter detection of a free-fall condition of the portable electronic apparatus.